How HD-DVD Works

Full DVD compatibility is a feature in all HD-DVD players, like this Toshiba HD-A1 player. See more HDTV pictures.­

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If you used to watch movies on videotape, you probably remember the first time you saw one on DVD. Suddenly, the video and sound were of much better quality. You could also pause without distorting the picture, skip from chapter to chapter and zoom in on the screen. When studios started adding commentary tracks, "extras" and multiple sound options on each disc, it seemed like the technology had reached its peak. People couldn't really imagine a better way to watch a recorded movie than on a DVD.

DVDs look best on screens that are smaller than 36 inches (91.4 centimeters), so they're not always up to the challenge of today's high-definition (HD) sets. To store and play HD movies, you need a disc that holds more information, like an HD-DVD. In this article, we'll explore how HD-DVDs differ from DVDs and what happened in the struggle between HD-DVD and Blu-ray.

­The basic idea behind the HD-DVD is really simple -- it looks like a DVD and acts like a DVD, but it holds more information. A DVD holds about two hours of standard definition video, but an HD-DVD can hold about 4 to 8 hours.

If you already know how DVDs work, then you already know a lot about HD-DVDs. A DVD stores information as a series of microscopic pits arranged in a very long spiral. A red laser reads these pits from the other side, so it sees them as bumps. The bumps reflect the laser's light to a sensor. Electronics within the DVD player read the information from the sensor as a digital signal. Check out How DVDs Work to learn more about how a DVD player does this.

This content is not compatible on this device.

A simplified view of what happens in a DVD player. An HD-DVD player is a lot like this, but it can send the signal digitally rather than converting it to analog.

An HD-DVD player is very similar to a DVD player, but it has a few notable differences. We'll look at them in the next section.

HD-DVD Facts

HD-DVD Capacity:

15 GB single layer, 30 GB dual layer

DVD Capacity:

4.7 GB single layer, 8.4 GB dual layer

Compression:

MPEG-2, MPEG-4, VC-1

High-definition Playback, 15 GB:

4 hours

High-definition Playback, 50 GB:

8 hours

HD-DVD Players

The difference between a red laser and a blue laser is like the difference between a fine-tipped pen and a magic marker.

An HD-DVD uses the same principles -- it contains a bumpy layer that reflects light from a laser to a sensor, creating a digital signal. HD-DVDs are even exactly the same size as DVDs (120 millimeters in diameter and 1.2 millimeters thick). But three important differences allow them to hold quite a bit more information than DVDs:

They use 405-nanometer blue-violet lasers rather than 650-nanometer red lasers.

The pits are smaller and the tracks are closer together.

They use more efficient compression to cut down the size of the files they store.

The color of the laser may seem like a trivial change to make, but the shorter wavelength of the blue-violet laser is what allows HD-DVD's pits to be smaller and arranged closer together. In other words, it allows the disc to have a much narrower track pitch. Regular DVDs have a track pitch of 0.74 micrometers, and HD-DVDs have a track pitch of 0.40 micrometers. You can imagine this as the difference between writing with a magic marker and a fine-tipped pen.

The other big difference between DVDs and HD-DVDs involves how the information on the disc is compressed. Most DVDs use MPEG-2 compression. HD-DVDs can use MPEG-2, but they typically use the more efficient MPEG-4, which allows higher video quality with a smaller file size. HD-DVDs can also use VC-1 (or Windows Media) compression.

Finally, because of general improvements in the technology, an HD-DVD player can read information from the disc and deliver it to the TV about three times as fast as a DVD player can. It can also send the signal to an HDTV digitally using a High Definition Multimedia Interface (HDMI), preventing the quality loss that conversion to analog causes.

One of the first questions people ask about HD-DVD (besides "Is it better than Blu-ray?") is whether their old DVDs are about to become obsolete. Let's take a look at what is likely to happen with players and discs as people upgrade.

Standard vs. High-definition

Wondering what the difference is between standard and high definition? Standard definition (SD) uses 525 lines of pixels from top to bottom. High definition (HD) uses up to 1125 lines. Not all of these lines are visible on the screen, but they're included as part of the signal.

DVD Compatibility

The blue laser sees through the outer layer, skipping straight to the high-definition content.

If you decided to buy an HD-DVD player the first day they hit the market, you'd still be able to play your DVDs on it. On the other hand, if you bought a new movie on HD-DVD, it wouldn't play in your old DVD player. Since an HD-DVD is exactly the same size and shape as a regular DVD, it's pretty easy to make new players that can handle both -- they just need a laser pickup that can read either format. The Toshiba HD-DVD player brought to market in April 2006 can read DVDs, HD-DVDs and CDs.

Even if HD-DVDs had gained widespread use, you would still have been able to buy DVDs -- the majority of homes in the United States don't have HDTVs, and there's no point in upgrading to HD-DVD without one. In addition, HD-DVDs can store regular and high-definition content on the same disc. Twin format discs have two layers -- a DVD layer on top uses a red laser, and an HD-DVD layer on the bottom uses a blue laser. The outer layer is transparent to the blue laser.

The other option for including DVD and HD-DVD content on the same disc is a combination format, which uses a two-sided disc. A red laser can read the DVD side, and a blue laser can read the HD-DVD side.

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To access the DVD content on a combination HD-DVD, simply flip the disc over.

With either option, you could buy one disc that would play in both DVD and HD-DVD players. If these discs had become available in stores, they would have been a good choice if you planned to upgrade to high-definition at some point in the future. Twin or combination discs would also have been useful for libraries and movie rental stores, since not everyone will be ready to upgrade their player right away. With the death of the HD-DVD format (more on that later), consumers must pin their hopes on a Blu-ray/DVD hybrid player.

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The HD-DVD format didn't have a lock on the high definition home video market. For a while, it competed with another format called Blu-ray. The war between HD-DVD and Blu-ray split the home video industry into two camps, each betting the other side's format would crumple. But how were the two formats different to begin with? Keep reading to find out.

Up-conversion

Regular DVDs generally have enough resolution to look good on 480-line analog displays, which isn't sufficient for new big-screen sets. The Toshiba HD-DVD player can automatically up-convert regular DVDs to accommodate 720- or 1080-line displays. The converted picture won't have all the resolution of an HD-DVD, but it will be better than an analog signal from a DVD player.

Blu-Ray vs. HD-DVD

The Xbox 360 HD-DVD player

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Several companies have developed alternatives to the existing DVD standard. For a few years, the two forerunners were HD-DVD and Blu-ray. Competition between the two escalated, drawing inevitable comparisons to the struggle between VHS and Betamax. Here are the highlights:

The DVD Forum, which creates DVD standards, approved HD-DVD and has not approved Blu-ray. Toshiba, the primary company behind the HD-DVD standard, has a seat on the DVD Forum Steering Committee.

Originally, HD-DVD was less expensive than Blu-ray, partly because HD-DVDs could be produced on pre-existing equipment, and Blu-ray discs can't. HD-DVD players originally sold for around $399, but dropped in price to around $290. Since then, companies have improved Blu-ray player manufacturing techniques. Today, you can find Blu-ray players for less than $300.

HD-DVD players hit the market on April 18, 2006, two months before the first Blu-ray player hit the U.S. market in June 2006.

­Along with other companies, Toshiba, Microsoft and Intel sided with HD-DVD. Microsoft released an add-on HD-DVD drive for its Xbox 360 in November 2006. The Blu-ray Disc Association, on the other hand, had electronics companies like Sony (which released the Blu-ray-equipped PSin November) and Pioneer, computer companies like Dell and Apple and entertainment companies like Disney and Fox on its board of directors. Most of the motion picture industry originally supported Blu-ray, in part because the need for new manufacturing equipment might cut down on piracy.

The battle raged for a couple of years before ending in 2008, but at the beginning the outcome wasn't a foregone conclusion. Critics of Blu-ray pointed out that the discs may have more capacity than any movie could ever use, even with special features. Many people initially thought that HD-DVD would be the winner solely because it was less expensive.

Eventually, the HD-DVD format succumbed in the format wars, and today the Blu-ray format reigns supreme in the HD market. How did this happen? Find out in the next section.

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Something Rotten in the State of HD

If you visit sites devoted to HD-DVD and Blu-ray, you might notice that something seems a little fishy with the supposed playback times. According to Toshiba, a 30 GB HD-DVD will hold eight hours of HD video. According to the Blu-ray disc association, a 50 GB Blu-ray disc will hold eight and a half hours of HD video. So how could a disk that's twice as big hold about half as much information?

The likeliest culprits for those numbers not adding up are bit rate and encoding. A file recorded at a low bit rate will take less space. In addition, many early Blu-ray tests used MPEG-2 encoding, which is less efficient than MPEG-4.

The Death of HD-DVD

The fall of the HD-DVD format means that retail chains like Best Buy no longer need to have two separate sections for high-definition media.

Blu-ray and HD-DVD had gone to war, and companies began to side with one format or the other. A few movie studios hedged their bets and produced content for both formats. But that wasn't very efficient or cost-effective. Retail stores faced a similar dilemma: should they dedicate vthe aluable floor space to both HD-DVD and Blu-ray? And if one failed, what would happen to the other? Many people agreed that it would be better for the industry to settle on one format.

By the summer of 2007, Blu-ray was doing very well. While dedicated Blu-ray player sales weren't very high, Sony's inclusion of a Blu-ray player in the PS3 helped promote the format. According to a report by Home Media Research, Blu-ray discs outsold HD-DVDs by a factor of two to one in the first half of 2007 [source: Reuters]. But HD-DVD wasn't ready to throw in the towel just yet. Despite the widening gap, studios like Paramount and Dreamworks announced that they would produce content exclusively for the HD-DVD format (although Steven Spielberg's Paramount films still found their way to Blu-ray) [source: Barnes].

Blu-ray achieved another victory that summer when Blockbuster Video stores switched exclusively to the Blu-ray format for its high-definition movie selection [source: Rusli]. And HD-DVD suffered yet another setback when the retail outlet Target announced it would stop carrying the HD-DVD players and only reserve space for Blu-ray machines [source: Ault]. After each announcement, a few bloggers and tech reporters pronounced the HD-DVD format officially dead. Yet HD-DVD backers continued to fight.

Professional reporters and amateur bloggers alike began to predict a format war that would stretch well into 2009 [source: Bangeman]. Companies that had hoped to build players that could handle both formats abandoned those plans. While the prognosis for HD-DVDs was grim, Toshiba's HD-DVD players were still less expensive than dedicated Blu-ray machines. The lower price gave HD-DVD supporters hope that they backed the right high-definition horse.

­But suddenly there was a shift to Blu-ray. More studios began to defect to Sony's format. By January of 2008, the end was near: Warner Bros. announced it was switching exclusively to Blu-ray. By that time, HD-DVD only had two studios backing its format: Universal and Paramount. To make matters worse, Universal's exclusivity agreement had just expired and Paramount had an escape clause. Paramount's agreement stated that if Warner Bros. jumped to Blu-ray, Paramount could follow suit [source: Fritz, Garrett].

But the tech world really knew HD-DVD was in trouble when Toshiba canceled all HD-DVD press conferences and events at the 2008 Consumer Electronics Show. HD-DVD still had a presence on the showroom floor, but Blu-ray's booth outshone its rival. The HD-DVD booth was shaped like a large square -- the Blu-ray booth took on the shape of a ghostly pirate ship. The writing was definitely on the wall.

A short time later, retail giant Wal-Mart announced it would only offer Blu-ray movies and electronics in its stores. Toshiba officially conceded the format war to Blu-ray in February 2008. The company announced it would stop manufacturing HD-DVD players by that March [source: Negishi, Hamada].

That wraps up the story on HD-DVD -- for now. To learn more about high definition video, tune in to the links on the next page.

I'm Not Dead Yet

The HD-DVD format may not be as dead as we thought. In China, manufacturers are throwing support behind CH-DVD, an offshoot of the HD-DVD format [source: Wong]. Will China's support resuscitate the format and reignite the war with Blu-ray?